A solid polymer fuel cell is comprised of a stack of single cells and two current collectors disposed on the outside of the stack. Each of the single cells consists of a solid polymer electrolyte membrane, two electrodes disposed on both sides of the solid polymer electrolyte membrane, and separators with gas-feeding grooves for feeding a fuel gas, such as hydrogen, and an oxidant gas, such as oxygen, to each of the electrodes.
The separators in the solid polymer fuel cell are required to have high levels of gas impermeability so as to allow the fuel gas and oxidant gas to be fed to the electrodes completely separately. In addition, the internal resistance of the battery is required to be minimized so as to achieve a high generation efficiency, and, for this reason, the separators are also required to be highly electrically conductive. Furthermore, in order to allow the heat accompanying the battery reaction to be efficiently dissipated and to obtain a uniform temperature distribution within the battery, the separators are required to have high thermal conductivity. To ensure long-term durability, the separators are also required to be highly corrosion-resistant. For these reasons, the separators in polymer electrolyte fuel cells are mainly made of stainless steel or carbon material.
The separators for fuel cells typically consist of a flat plate with a plurality of parallel grooves formed on one or both sides thereof. This configuration is adopted so as to ensure that the water produced in the grooves during electricity generation can be discharged, as well as to allow the electricity generated by a catalyst electrode in the fuel battery cell to be transmitted to the outside. The grooves are also used as channels for a reaction gas to flow into the fuel battery cell.
Normally, the fuel cell separator is made of a carbon or metal plate. To provide the plate with the gas channels, a carbon plate is generally mechanically machined, while a metal plate is generally press-molded. However, these techniques for providing gas channels have been problematic in that, for example: (1) the degree of freedom in the shape of the channel is small; (2) sufficient supply of gases below ribs cannot be ensured; (3) contact resistance is large; (4) flooding tends to occur under the ribs (namely, diffusion polarization is large); and (5) removal of the produced water is insufficient and cell performance is instable.
These problems are caused for the following reasons, for example. (1) When a carbon plate or a metal plate is used, as in the prior art, the shape of the channel is limited by machining or molding accuracies. As a result, fine shapes that would be resistant to flooding or drying-up cannot be realized. (2) In the exiting structures where the ribs are bulky, the issue of how to smoothly feed gases below the ribs, where the greatest amount of gas supplies are required, cannot be solved. (3) In the existing methods, the diffusion layer and the separator can only be formed as separate components, and the problem of contact resistance between the diffusion layer and the rib portion arises. (4) With the existing machining methods, it is difficult to selectively make only the portion below the ribs, where the amount of water produced is greatest, water repellent, thereby preventing improvements in drainage and cell performance. (5) In the existing methods, the separator is only partially provided with water-repellency or hydrophilic property, so that drainage cannot be performed in a detailed manner, resulting in a decrease in cell performance.